EXPERIMENTAL METHODS

Extraction and Bulk Parameters

Sediments were stored at <0°C prior to freeze-drying and homogenization. Aliquots of the dry sediment were taken for total carbon (TC) and sulfur (TS) analysis using a Leco carbon analyzer. A further aliquot of dry sediment was fired to remove organic carbon (500°C for 24 hr) and carbon content determined to give total inorganic carbon (TIC). It is assumed that all inorganic carbon consists of calcite so that CaCO3 = TIC × 8.3334. Organic carbon content (Corg) was determined by difference (Corg = TC - TIC). Further aliquots of dry sediment (~3 g) had a known quantity of an internal standard (n-C36 alkane) added for later quantification and were extracted into dichloromethane/methanol (3:1) (6 × 3 mL extractions) with ultrasonication (15 min). Samples were centrifuged following each extraction and decanted. Combined extracts were dried under N2 onto silica (0.5 g; 70-230 mesh) ready for column chromatography.

Compound Class Fractionation

Column chromatography was conducted on each sample after the methods of Peltzer et al. (1984). The column was packed with deactivated (5%) silica (7 g of 70-230 mesh in a 9-mm internal diameter [ID] column) in hexane. Four fractions were collected following elution with (1) hexane (20 mL), (2) hexane/toluene (4:1; 30 mL), (3) hexane/ethyl acetate (37:3; 40 mL), and (4) hexane/ethyl acetate (4:1; 40 mL). Excess solvent was removed by rotary evaporation and fractions were transferred in dichloromethane to vials, dried under N2, and stored at ~4°C until analysis.

Lipid Analysis

Fractions 1-3 were analyzed directly without prior derivatization. Fraction 4 contained alcohol and acid moieties that were derivatized to their trimethylsilyl ethers with bis-(trimethylsilyl) trifluoroacetamide (BSTFA) in dichloromethane (100 µL of each at 70°C for 2 hr in N2-purged vials). Quantification was made by gas chromatography with on-column injection and flame ionization detection (GC-FID) using an HP1 fused silica capillary column (60 m × 0.32 mm ID). Hydrogen was used as a carrier gas and the oven temperature program was 45° to 145°C at 10°C/min and 145° to 305°C at 4°C/min. Data acquisition and integration were made with an Atlas data system. Gas chromatography-mass spectrometry was performed using a Hewlett-Packard 5972 quadrapole mass spectrometer. Split-splitless injection was used with an HP1 fused silica capillary column (30 m × 0.32 mm ID; the subsequent loss of resolution by using a shorter column was compensated by minimizing column bleed above 280°C). Helium was used as a carrier gas with the same oven-temperature program as used for GC-FID. The mass spectrometer was operated in electron impact (ionizing energy of 70 eV; ion source temperature of 250°C) with a scan time (m/z 50-600) of 1 s. Compound identification was made by comparing mass spectra with authentic standards, literature sources, and relative retention times.